Characterization of the cervical spine as stable or unstable is frequently an important part of diagnosing and treating the several hundred thousand patients with cervical spine disorders. This characterization of the spine is particularly important in determining whether to treat the patient using surgery and monitoring the success of the surgery. Despite the accepted, profound importance of spinal stability in many patients, a rigorous definition of stability is usually not available and there are no validated measurements of stability that clinicians commonly use in their day-to-day practice. The lack of readily available, validated measures of spinal stability makes it difficult to establish optimum treatment algorithms or to scientifically compare different treatments. Numerous investigators have explored methods to document spinal stability, but none of these methods have made it to routine clinical practice. An innovative, validated method to quantify cervical spine stability and correlate those measures to clinical symptoms, which could be used in routine clinical practice, has been developed by the applicant company. The technology includes a motion control device to reduce sources of errors, pain feedback sensors to help physicians understand the relationship between pain and spine position, and software to quantify the motion of individual vertebra, calculate relative motion, and provide a simple clinical report. The specific aims of Phase I are to provide data that can help clinicians interpret the quantitative measurements of intervertebral motion and to provide evidence that the dynamic fluoroscopic imaging can replace conventional flexion and extension x-rays in Phase II prospective randomized clinical studies. These aims will be accomplished by collecting and analyzing cervical spine stability measurements in 50 asymptomatic subjects and 50 patients with cervical spine disorders. A clinically efficacious method to quantify cervical spine stability could benefit hundreds of thousands of patients. [unreadable] [unreadable]